The present invention relates to a phase error measuring method, an MR imaging method, and a magnetic resonance imaging (MRI) apparatus. More particularly, the present invention is concerned with a phase error measuring method for measuring a phase error that occurs in each phase encoding direction corresponding to the direction of a readout magnetic field gradient that is turned in units of a radian, an MR imaging method of performing a main scan by compensating phase errors, and an MRI apparatus in which the methods are implemented.
Patent Document 1 and Patent Document 2 have disclosed an MR imaging method in which a compensatory component intended to suppress an adverse effect on a spin echo, which succeeds a spin echo derived from application of a phase-encoding magnetic field gradient, caused by remanent magnetization or eddy currents attributable to the phase encoding magnetic field gradient is applied as a compensatory pulse before, after, or before and after application of either the phase encoding magnetic field gradient or a rewinding magnetic field gradient, and an MR imaging method of applying the compensatory component to the magnetic field gradient itself.
Moreover, Patent Document 3 has disclosed an MR imaging method capable of suppressing an adverse effect on a spin echo, which succeeds a spin echo derived from application of a phase encoding magnetic field gradient, caused by remanent magnetization or eddy currents attributable to the phase encoding magnetic field gradient, and capable of suppressing an adverse effect on the spin echo derived from the application of the phase encoding magnetic field gradient.
Moreover, conventional MR imaging methods include a method called as a PROPELLER (Periodically Rotated Overlapping Parallel Lines with Enhanced Reconstruction) method. In general, the PROPELLER method is employed in combination with a fast spin echo (FSE) imaging technique. According to the PROPELLER method, a unit called a blade is employed, and data acquired in units of a blade according to the FSE imaging technique is defined in a K-space. The blade is turned with the origin of the K-space as a center in order to produce data (an imaging method in which a data filling trajectory along with data is defined in the K-space is turned with the origin of the K-space as a center). Consequently, the resultant blades of data items are used to correct motion data highly accurately. This imaging method can largely reduce artifacts affecting imaging of a patient who makes motions.
[Patent Document 1] Japanese Unexamined Patent Publication No. 8(1996)-322817
[Patent Document 2] Japanese Unexamined Patent Publication No. 10(1998)-75940
[Patent Document 3] Japanese Unexamined Patent Publication No. 2002-143115
However, according to the conventional PROPELLER method, a readout magnetic field gradient is turned in units of a radian. Although a phase error occurs in a phase encoding direction along with the turning of the readout magnetic field gradient, the phase error is not compensated. This poses a problem in that when image data is acquired by performing a main scan, an accurate phase encoding quantity is not applied in every phase encoding direction.